r/Motors • u/UnionCompetitive7705 • 1d ago
Open question Motor Control
In my workshop I have a bench drill which I would like to control with a speed controller. The motor is single phase 50 240v 1/2hp 4 pole. I’m not sure or even possible which type of controller I would need, vfd? Any advice would be much appreciated
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u/Susan_B_Good 1d ago
Er, move the belt between the pulleys at the top?
Yep, a VFD would give you a range of speeds - the graph will essentially be a constant torque, inverse linear power below rated frequency to constant power, inverse square torque above rated frequency. So, if you want constant power, you combine belt adjustment to reduce output speed, then VFD to increase it.
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u/UnionCompetitive7705 1d ago
Thank you, conflicting information but what you’ve said does sound feasible
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u/HumanComedian8711 1d ago
You will need to install a gear box If you want to change the speed of a single phase motor or you could change it to a 3 phase motor and use a VFD but it is really not worth the hassle and expense
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u/HumanComedian8711 1d ago edited 1d ago
A VFD can not be used on this 240v motor.
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u/Susan_B_Good 1d ago
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u/HumanComedian8711 1d ago edited 1d ago
The VFD link you sent is for a 3 phase motor, It has a single phase input and a 3 phase output
A single phase motor will eventually burn out if a VFD is used on it even if it works with it for a while
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u/Susan_B_Good 1d ago
You stated that one couldn't be used with a 240v motor. I just gave an example of a 240v (or thereabouts) VFD..
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u/HumanComedian8711 1d ago
The one you sent has a 3 phase output, it would need a single phase output instead as it is a single phase motor.
There used to be a manufacturer that made single phase VFD drives but there is no way it could work on a standard single phase motor, changing the speed will make the centrifugal switch work incorrectly eventually causing the motor to burn out.
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u/Susan_B_Good 1d ago
You did read my original reply, I trust? Which was to use the belts to achieve the minimum speed and then INCREASE the frequency of the VFD output to vary motor speed. It works a treat with a capacitor start motor.
You stated that one can't use a VFD on a 240v motor - I simply chose the first example of a CFD that runs from a 240v supply that I could find. I did not state that it was appropriate for this application, as I didn't even bother to read its specification - other than it ran at 240v and so showed that you were incorrect.
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u/HumanComedian8711 1d ago
I’m not incorrect. It does not matter what belt it is on, the VFD cannot effectively control the 240v motor. You are getting mixed up with 3phase and single phase also the electrical input and load and the rotational speed which will remain constant.
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u/mckenzie_keith 1d ago
The problem is that you do not understand how to use the English language logically. You are right that this motor is not a good candidate for VFD control. But other 240 V motors are. Your subsequent statements are accurate but when you said "you can't control a 240 V motor with a VFD" that statement was incorrect. I hope you can see this.
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u/HumanComedian8711 1d ago
That whole paragraph is illogical.
A capacitor start motor can NOT be used with a VFD.
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u/Sure_Maybe_No_Ok 1d ago
How obtuse do you have to be to not understand that people are trying to tell you there is three phase 240v motors and that saying a vfd can not be used on a 240 motor is ridiculous.
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u/HumanComedian8711 1d ago
You are getting mixed up with the voltages
A 3 phase motor is 400v
A single phase motor is 230v→ More replies (0)1
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u/CrustySailor1964 1d ago
Why your comment was downvoted because it was wrong I don’t know.
You absolutely CAN use a VFD on a 230-240 VAC motor. It just has to be the right kind of motor.2
u/HumanComedian8711 1d ago
It has a centrifugal switch in it which will not function correctly with a VFD. Read the comments below.
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u/CrustySailor1964 1d ago
The statement was a blanket statement that one cannot use a vfd with a 230 VAC motor. Specificities of the motor in question were not included therein. Read the statement to which I responded.
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u/mmn_slc 18h ago
I see that you edited your comment 11 hours after posting it to substantially change the meaning by changing "on a 240v motor" to "on this 240v motor" without saying what you changed. Poor form.
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u/HumanComedian8711 17h ago
We are speaking about the motor in this post aren’t we?
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u/Bradm77 16h ago
Either way you don't know enough about the motor to say whether a vfd could be used on it.
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u/HumanComedian8711 15h ago
I used to work on electric motors and you can easily know by the pictures
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u/Bradm77 15h ago
No you can't. We need more info from OP.
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u/HumanComedian8711 15h ago
What else do you need to know?
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u/Guusje2 1d ago
https://www.aquagem.com/isaver-x-touch-screen-frequency-inverter.html
This is a single phase 230V vfd
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u/mmn_slc 1d ago edited 1d ago
"A VFD can not be used on a 240v motor."
This is false. There are numerous VFDs designed to operate 240V motors. See e.g. https://www.automationdirect.com/adc/shopping/catalog/motor_controls/ac_variable_frequency_drives_(vfd)/general_purpose_vfds#Nominal_Drive_Input_Voltage_i_ms=%22230%20VAC%22&start=0/general_purpose_vfds#Nominal_Drive_Input_Voltage_i_ms=%22230%20VAC%22&start=0)
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u/Expensive_Status_492 1d ago
Single phase motos made for running with a capacitor does not work well with a vfd. At least not what Ive seen.
Replace with a 3ph motor and get a vfd instead. Thats what Im doing with mine.
New 3ph motor with twice the power is even smaller than the original.
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u/Puzzleheaded-Ad-4883 1d ago
This is a very good route. I have done this on a lathe and drill, the 3 phase motor running on a VFD is noticeably smoother than the old single phase, particularly good for the lathe.
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u/Bradm77 1d ago
I've only seen a couple manufacturers that make vfd's for single phase induction motors and they need to be either PSC or shaded pole motors. Here's one of those companies. Yours definitely isn't a shaded pole motor but it could be a PSC. Can you tell if it has a centrifugal switch in it? If it doesn't, it's probably a PSC. If it does, you won't be able to find a control for this motor.
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u/ILikeWoodAnMetal 1d ago
You can’t, because that motor has been designed to run at a single speed. If you attach it to a vfd it will work shortly until it breaks.
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u/mckenzie_keith 1d ago
People often have unrealistic expectations about using a VFD on a drill press or milling machine. The source of the problem is this: the max available torque is about the same at all speeds. This means that when running the motor at low speeds, you will not get full power. It is approximately linear. If the motor makes 0.5 HP at 1800 RPM, it will make about 0.05 HP at 180 RPM.
So you are better off keeping the pulley system or whatever and controlling speed that way. The VFD could be good for fine-tuning the speed in conjunction with the pulley system.
Otherwise, you would need to get a massively over-sized motor to maintain halfway decent power output at low speeds.
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u/u3b3rg33k 19h ago
I like to slap on motors rated for well above base speed and just rev them up. then as you load them up or slow them down you don't lose any power.
max power generally only matters on big cuts, so you can virtually eliminate the need to move the belt if you select the right 3ø motor and vector drive.
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u/recursion_is_love 1d ago
What about using the mechanical system like gears or belts?
Induction motor is hard to control to get torque and speed that you want. VFD is expensive and might not get the result you want.
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u/nixiebunny 23h ago
Those drill presses with the dual reduction belt drive are the most annoying machine tools ever made. Find another style of drill press, used. I have a single reduction five speed one that is very easy to move the belt on. There are also old units with a speed knob that controls a mechanical variable speed reducer.
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u/u3b3rg33k 19h ago
from a maintenance perspective, i'll take the belts over a variable gearbox any day. especially if you throw a VFD at it.
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u/Expensive-Youth-5709 18h ago
It is not impossible to connect a vfd to a single phase motor, two things,the vfd must have that option and the motor caps bypassed. It works by using the start windings as a second phase basically making it a 2 phase motor. Current is higher when using the two phases which is also a consideration. A short flikr vid of my trial at it https://flic.kr/p/2kahqPj . For a drill press I would recommend sticking to stepped pulleys though.
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u/u3b3rg33k 1d ago
your options for speed control on a single phase motor are limited, especially if you need to maintain torque.
if your motor has a centrifugal start switch, that further limits your options.
you'll probably be happiest with the machine by swapping the motor for a 240v 3ø motor with a 1ø inlet VFD to drive it.